Solid-state imaging device, method of making the same, and imaging apparatus

ABSTRACT

A solid-state imaging device includes the following elements. A photoelectric conversion section is arranged in a semiconductor layer having a first surface through which light enters the photoelectric conversion section. A signal circuit section is arranged in a second surface of the semiconductor layer opposite to the first surface. The signal circuit section processes signal charge obtained by photoelectric conversion by the photoelectric conversion section. A reflective layer is arranged on the second surface of the semiconductor layer opposite to the first surface. The reflective layer reflects light transmitted through the photoelectric conversion section back thereto. The reflective layer is composed of a single tungsten layer or a laminate containing a tungsten layer.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.11/945,717, filed Nov. 27, 2007, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication No. 2006-331559 filed in the Japanese Patent Office on Dec.8, 2006, the entirety of which is incorporated by reference herein tothe extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a back-illuminated solid-state imagingdevice, a method of making the same, and an imaging apparatus includingthe solid-state imaging device.

2. Description of the Related Art

Referring to FIG. 8, a back-illuminated solid-state imaging deviceincludes a silicon substrate 211, in which photodiodes 221 are arranged,and a signal circuit section 231. Light is incident on a first surfaceof the silicon substrate 211. The signal circuit section 231 is arrangedin a second surface of the silicon substrate 211. Assuming that thethickness of a silicon layer in a portion corresponding to eachphotodiode 221 is several micrometers or less, incident light componentshaving long wavelengths are not sufficiently absorbed by the photodiodes221 and are transmitted to the signal circuit section 231 in the secondsurface of the silicon substrate 211. Particularly, light componentshaving long wavelengths (e.g., red wavelengths) are transmitted in aportion corresponding to each photodiode 221 and the transmitted lightcomponents enter the signal circuit section 231. Disadvantageously, itis difficult to efficiently convert light in a long wavelength range(hereinafter, long-wavelength light) into an electrical signal.Furthermore, the transmitted light is reflected by an interconnectionlaminate 233 in the signal circuit section 231, so that the reflectedlight is incident on the photodiodes in surrounding pixels, leading tocrosstalk. Unfortunately, the occurrence of crosstalk causes a problem.For example, Japanese Unexamined Patent Application Publication No.2006-261372 discloses a related-art solid-state imaging device having astructure in which a polysilicon layer and an aluminum layer arearranged on photodiodes. In this structure, it is insufficient to shieldagainst long-wavelength light components, such as infrared light andnear-infrared light. Particularly, the amount of transmitted light inthe polysilicon layer is large. The aluminum layer is formed by graingrowth. Disadvantageously, light is leaked from grain boundaries, thusreducing the reflectance.

SUMMARY OF THE INVENTION

Problems to be solved include the difficulty to efficiently convertlong-wavelength light transmitted through each photoelectric conversionsection (e.g., each photodiode) into electrical signals and aninsufficient effect in shielding light, particularly, long-wavelengthlight, the effect being produced by arranging the polysilicon layer andthe aluminum layer for light reflection on one surface of eachphotodiode opposite to the other surface on which light is incident.

It is desirable to improve sensitivity while efficiently convertinglong-wavelength light transmitted through each photodiode intoelectrical signals.

According to an embodiment of the present invention, a solid-stateimaging device includes the following elements. A photoelectricconversion section is arranged in a semiconductor layer having a firstsurface through which light enters the photoelectric conversion section.A signal circuit section is arranged in a second surface of thesemiconductor layer opposite to the first surface thereof. The signalcircuit section processes signal charge obtained by photoelectricconversion by the photoelectric conversion section. A reflective layeris arranged on the second surface of the semiconductor layer opposite tothe first surface. The reflective layer reflects light transmittedthrough the photoelectric conversion section back thereto. Thereflective layer is composed of a single tungsten layer or a laminatecontaining a tungsten layer.

According to this embodiment, the reflective layer that reflects lighttransmitted through the photoelectric conversion section back thereto isarranged on the second surface of the semiconductor layer opposite tothe first surface through which light enters the photoelectricconversion section. If light entering the photoelectric conversionsection is not completely absorbed by the photoelectric conversionsection, the reflective layer can reflect the transmitted light,particularly, long-wavelength light components, such as near-infraredlight and infrared light, which are easily transmitted through thephotoelectric conversion section, back to the photoelectric conversionsection. In other words, light which has been transmitted once throughthe photoelectric conversion section can be received again by thephotoelectric conversion section. Consequently, the amount of light, inparticular, long-wavelength light components, received by thephotoelectric conversion section can be substantially increased.Advantageously, the sensitivity of the photoelectric conversion sectionto long-wavelength light components can be improved. Since thereflective layer is composed of the single tungsten layer or thelaminate containing the tungsten layer, the density of the reflectivelayer is higher than that of a reflective layer including an aluminumlayer formed by grain growth. Accordingly, this high-density reflectivelayer can reflect long-wavelength light components, particularly,near-infrared light and infrared light. Furthermore, among lightincident on the first surface of the semiconductor layer, lightcomponents which are not absorbed by the photoelectric conversionsection are reflected back to the photoelectric conversion section bythe reflective layer on the second surface in which the signal circuitsection is arranged, thus preventing crosstalk caused by the leakage oflight into surrounding pixels.

According to another embodiment of the present invention, a method ofmaking a solid-state imaging device includes the steps of (a) forming aphotoelectric conversion section in a semiconductor layer having a firstsurface through which light enters the photoelectric conversion section,and (b) forming a signal circuit section in a second surface of thesemiconductor layer opposite to the first surface, the signal circuitsection including transistors for extracting an electrical signalobtained by photoelectric conversion by the photoelectric conversionsection. The step (b) includes the substep of forming a contact portionconnected to each transistor in the signal circuit section. In thesubstep, a reflective layer is formed on the second surface of thesemiconductor layer opposite to the first surface, the reflective layerreflecting light transmitted through the photoelectric conversionsection back thereto and being composed of a single tungsten layer or alaminate containing a tungsten layer.

According to this embodiment, in the substep of forming a contactportion connected to each transistor in the signal circuit section, thereflective layer that reflects light transmitted through thephotoelectric conversion section back thereto is formed on the secondsurface of the semiconductor layer opposite to the first surface.Accordingly, if light entering the photoelectric conversion section isnot completely absorbed by the photoelectric conversion section,particularly, long-wavelength light components, such as near-infraredlight and infrared light, which are easily transmitted through thephotoelectric conversion section, can be reflected back to thephotoelectric conversion section by the reflective layer. In otherwords, light which has been transmitted once through the photoelectricconversion section can be received again by the photoelectric conversionsection. Consequently, the amount of light, in particular,long-wavelength light components, received by the photoelectricconversion section can be substantially increased. Advantageously, thesolid-state imaging device in which the sensitivity of the photoelectricconversion section to long-wavelength light components is improved canbe made. Since the reflective layer is composed of the single tungstenlayer or the laminate containing the tungsten layer, the density of thereflective layer is higher than that of a reflective layer including analuminum layer formed by grain growth. Accordingly, this high-densityreflective layer can reflect long-wavelength light components,particularly, near-infrared light and infrared light. Furthermore, amonglight incident on the first surface of the semiconductor layer, lightcomponents which are not absorbed by the photoelectric conversionsection are reflected back to the photoelectric conversion section bythe reflective layer on the second surface in which the signal circuitsection is arranged. Consequently, the solid-state imaging device whichprevents crosstalk caused by the leakage of light into surroundingpixels can be made.

According to another embodiment of the present invention, an imagingapparatus includes the following elements. A collection optical unitcollects incident light. A solid-state imaging device receives the lightcollected by the collection optical unit and converts the light into anelectrical signal. A signal processing unit processes the electricalsignal. The solid-state imaging device includes the following elements.A photoelectric conversion section is arranged in a semiconductor layerhaving a first surface through which light enters the photoelectricconversion section. A signal circuit section is arranged in a secondsurface of the semiconductor layer opposite to the first surface. Thesignal circuit section extracts the electric signal obtained by thephotoelectric conversion section. A reflective layer is arranged on thesecond surface of the semiconductor layer opposite to the first surface.The reflective layer reflects light transmitted through thephotoelectric conversion section back thereto. The reflective layer iscomposed of a single tungsten layer or a laminate containing a tungstenlayer.

According to this embodiment, the imaging apparatus includes thesolid-state imaging device according to the foregoing embodiment. Asdescribed above, in the imaging apparatus, the sensitivity is high andcrosstalk can be prevented.

According to the embodiment first described above, the solid-stateimaging device having the following advantages can be realized. Sincethe reflective layer that reflects light transmitted through thephotoelectric conversion section back thereto and is composed of thesingle tungsten layer or the laminate containing the tungsten layer isarranged on the second surface of the semiconductor layer opposite tothe first surface through which light enters the photoelectricconversion section, the sensitivity of the photoelectric conversionsection to long-wavelength light components can be improved to obtainhigh sensitivity and prevent crosstalk. The amount of light entering thephotoelectric conversion section can be increased to provide a highdynamic range.

According to the embodiment second described above, the solid-stateimaging device having the following advantages can be made. Since thereflective layer that reflects light transmitted through thephotoelectric conversion section back thereto and is composed of thesingle tungsten layer or the laminate layer containing the tungstenlayer is arranged on the second surface of the semiconductor layeropposite to the first surface through which light enters thephotoelectric conversion section, the sensitivity of the photoelectricconversion section to long-wavelength light components can be improvedto obtain high sensitivity and prevent crosstalk. The amount of lightentering the photoelectric conversion section can be increased toprovide a high dynamic range.

According to the embodiment third described above, since the imagingapparatus includes the solid-state imaging device according to theforegoing embodiment, the same advantages as those described above canbe obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a solid-state imagingdevice according to an embodiment (first embodiment) of the presentinvention;

FIG. 2 is a schematic cross-sectional view of a solid-state imagingdevice according to an embodiment (second embodiment) of the presentinvention;

FIG. 3 is a schematic cross-sectional view of a solid-state imagingdevice according to an embodiment (third embodiment) of the presentinvention;

FIGS. 4A and 4B are layout plan views of the solid-state imaging deviceaccording to the embodiment (third embodiment) of the present invention;

FIG. 5 is a schematic cross-sectional view of a solid-state imagingdevice according to an embodiment (fourth embodiment) of the presentinvention;

FIG. 6 is a schematic cross-sectional view of a solid-state imagingdevice according to an embodiment (fifth embodiment) of the presentinvention;

FIG. 7 is a block diagram illustrating an imaging apparatus according toan embodiment (application) of the present invention; and

FIG. 8 is a schematic cross-sectional view of a related-art solid-stateimaging device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A solid-state imaging device 1 according to an embodiment (firstembodiment) of the present invention will now be described withreference to FIG. 1 which is a schematic cross-sectional view of thesolid-state imaging device 1.

Referring to FIG. 1, pixel isolation regions 12 for isolating a pixelare arranged in a semiconductor layer 11. The semiconductor layer 11includes, for example, a silicon layer or a silicon substrate. Eachpixel isolation region 12 includes, for example, a p-type well region.In each area partitioned by the pixel isolation regions 12, aphotoelectric conversion section 21 is arranged. On a first surface,through which light enters, of each photoelectric conversion section 21(the lower surface of the photoelectric conversion section 21 in FIG.1), i.e., in a first surface of the semiconductor layer 11 through whichlight enters the photoelectric conversion section 21, a hole storagelayer 22 is arranged. The hole storage layer 22 includes, for example, ap+ region. A second surface of the photoelectric conversion section 21(the upper surface of the photoelectric conversion section 21 in FIG. 1)opposite to the first surface thereof, i.e., a second surface of thesemiconductor layer 11 opposite to the first surface thereof includes ahole storage layer 23. Under the hole storage layer 23, an n-type wellregion 24 is arranged. The hole storage layer 23 includes, for example,a p+ region. In addition, a gate electrode (for example, a transfergate) 32 is arranged over the second surface of the photoelectricconversion section 21, with a gate insulation layer 31 therebetween. Inthe semiconductor layer 11, an n+ region 25 is arranged adjacent to oneend of the gate electrode 32, with the gate insulation layer 31therebetween.

A contact portion 41 is connected to each gate electrode 32. Anothercontact portion 42 is connected to each pixel isolation region 12. Areflective layer 43, serving as a contact portion similar to the contactportions 41 and 42, is arranged over each photoelectric conversionsection 21, with the gate insulation layer 31 therebetween. In addition,contact portions connected to other transistors, for example, gateelectrodes and source and drain regions in a signal circuit section (notshown) are arranged. The gate insulation layer 31 and the gateelectrodes 32 are overlaid with an insulation layer 81. Theabove-described contact portions are formed by filling holes 91, 92, and93 arranged in the insulation layer 81 with, for example, a conductivematerial.

The reflective layer 43 has to reflect light transmitted through eachphotoelectric conversion section 21 toward the section 21. Accordingly,the reflective layer 43 includes a material that reflectslong-wavelength light components, such as near-infrared light andinfrared light, toward the photoelectric conversion section 21. Thereflective layer 43 may reflect shorter-wavelength light components,such as visible light, near-ultraviolet light, and ultraviolet light, inaddition to the long-wavelength light components. Examples of thematerials having the above-described characteristics include tungsten.It is therefore preferred that the reflective layer 43 be composed of asingle tungsten layer. Alternatively, it is preferred that thereflective layer 43 be composed of a laminate containing a tungstenlayer. Examples of the laminates include a laminate containing apolysilicon layer and a tungsten layer and a laminate including atungsten layer and a silicide layer.

Since the reflective layer 43 includes the tungsten layer, lighttransmitted through the photoelectric conversion section 21 can bereflected toward the photoelectric conversion section 21. The tungstenlayer is formed without grain growth for an aluminum layer used in therelated art. Accordingly, grain boundaries are hardly generated.Consequently, the reflective layer 43 can reflect long-wavelength lightcomponents, such as near-infrared light and infrared light, which leakfrom grain boundaries in the aluminum layer.

Further, first interconnection lines 51 to 53 respectively connected tothe contact portions 41 and 42 and the reflective layer 43 are arranged.It is preferred that each first interconnection line 53 connected to thereflective layer 43 have a shape larger than, for example, the shape ofthe reflective layer 43 in plan view. Further, it is preferred that thefirst interconnection lines 51 and 52 be composed of, for example,tungsten. The first interconnection lines 51 and 52 may be composed ofanother metallic material, e.g., copper or aluminum. For example, whenthe first interconnection lines 51 to 53 are formed using tungsten,light which is not reflected by the reflective layer 43, for example,long-wavelength light components leaking from the periphery of each areacorresponding to the reflective layer 43 can be reflected toward thecorresponding photoelectric conversion section 21 by the firstinterconnection lines 51 to 53.

Each first interconnection line 51 is connected to a secondinterconnection line 51 through a via hole 54. Each firstinterconnection line 52 is connected to a second interconnection line 62through a via hole 55. Each first interconnection line 53 is connectedto a second interconnection line 63 through a via hole 56. Similarly,each second interconnection line 61 is connected to a thirdinterconnection line 71 through a via hole 64. Each secondinterconnection line 62 is connected to a third interconnection line 72through a via hole 65. Each second interconnection line 63 is connectedto a third interconnection line 73 through a via hole 66. Thesolid-state imaging device 1 of FIG. 1 includes an interconnectionlaminate having three interconnection layers. The present embodiment ofthe invention may be applied to a solid-state imaging device includingan interconnection laminate having four or more interconnection layers.An insulation layer 80, including the insulation layer 81, is arrangedso as to cover the above-described interconnection layers. Theinsulation layer 80 includes a plurality of insulation sublayers inaccordance with the arrangement state of interconnection. The secondsurface of the semiconductor layer 11 is overlaid with the signalcircuit section (not shown) which includes transistors, such as transfertransistors, reset transistors, and amplifier transistors, and theinterconnection laminate including the first interconnection lines 51 to53, the via holes 54 to 56, the second interconnection lines 61 to 63,the via holes 64 to 66, and the third interconnection lines 71 to 73.

In the solid-state imaging device 1 according to the first embodiment,the reflective layer 43 for reflecting light transmitted through eachphotoelectric conversion section 21 toward the section 21 is arrangedadjacent to the second surface of the photoelectric conversion section21 opposite to the first surface thereof, i.e., the second surface ofthe semiconductor layer 11 opposite to the first surface thereof. Iflight entering the photoelectric conversion section 21 is not completelyabsorbed by the photoelectric conversion section 21, particularly,long-wavelength light components that are easily transmitted througheach photoelectric conversion section 21, e.g., near-infrared light andinfrared light can be reflected back to the photoelectric conversionsection 21 by the reflective layer 43. In other words, light transmittedonce through the photoelectric conversion section 21 can be receivedagain by the photoelectric conversion section 21. Consequently, theamount of, particularly, long-wavelength light components received bythe photoelectric conversion section 21 is substantially increased.Thus, the sensitivity of the photoelectric conversion section 21 tolong-wavelength light components can be improved. Since the reflectivelayer 43 is composed of the single tungsten layer or the laminatecontaining the tungsten layer, the density of the reflective layer 43 ishigher than that of an aluminum layer formed by grain growth.Accordingly, the reflective layer 43 can reflect, in particular,long-wavelength light components, such as near-infrared light andinfrared light. Furthermore, among light incident on the first surfaceof the semiconductor layer 11 (i.e., the first surface of thephotoelectric conversion section 21), light components which are notabsorbed by each photoelectric conversion section 21 are reflected backto the photoelectric conversion section 21 by the reflective layer 43included in the signal circuit section in the second surface of thesemiconductor layer 11, thus preventing crosstalk caused by the leakageof light into surrounding pixels.

To make the solid-state imaging device 1 according to the firstembodiment, the contact portion 41 is formed on each gate electrode 32and the contact portion 42 is formed on each pixel isolation region 12.Simultaneously, the reflective layer 43, serving as a contact portionsimilar to those contact portions 41 and 42, may be formed over eachphotoelectric conversion section 21, with the gate insulation layer 31therebetween. For example, the holes 91 and 92 in the insulation layer81 are filled with tungsten to form the contact portions 41 and 42.Simultaneously, the hole 93 in the insulation layer 81 over eachphotoelectric conversion section 21 is filled with tungsten, thusforming the reflective layer 43.

A solid-state imaging device 2 according to an embodiment (secondembodiment) of the present invention will now be described withreference to FIG. 2, which is a schematic cross-sectional view of thesolid-state imaging device 2. The second embodiment relates to anexample of a countermeasure against a problem that it is difficult tofill the hole 93 for the reflective layer 43 with tungsten in accordancewith the first embodiment when the diameter of the hole 93 is large.

Referring to FIG. 2, pixel isolation regions 12 for isolating a pixelare arranged in a semiconductor layer 11. The semiconductor layer 11includes, for example, a silicon layer. Each pixel isolation region 12includes, for example, a p-type well region. In each area partitioned bythe pixel isolation regions 12, a photoelectric conversion section 21 isarranged. On a first surface, through which light enters, of eachphotoelectric conversion section 21 (the lower surface of thephotoelectric conversion section 21 in FIG. 2), i.e., in a first surfaceof the semiconductor layer 11 through which light enters thephotoelectric conversion section 21, a hole storage layer 22 isarranged. The hole storage layer 22 includes, for example, a p+ region.A second surface of the photoelectric conversion section 21 (the uppersurface of the photoelectric conversion section 21 in FIG. 2) oppositeto the first surface thereof, i.e., a second surface of thesemiconductor layer 11 opposite to the first surface thereof includes ahole storage layer 23. Under the hole storage layer 23, an n-type wellregion 24 is arranged. The hole storage layer 23 includes, for example,a p+ region. In addition, a gate electrode (for example, a transfergate) 32 is arranged over the second surface of the photoelectricconversion section 21, with a gate insulation layer 31 therebetween. Inthe semiconductor layer 11, an n+ region 25 is arranged adjacent to oneend of the gate electrode 32, with the gate insulation layer 31therebetween.

A contact portion 41 is connected to each gate electrode 32. Anothercontact portion 42 is connected to each pixel isolation region 12. Areflective layer 43, serving as a contact portion similar to the contactportions 41 and 42, is arranged over each photoelectric conversionsection 21, with the gate insulation layer 31 therebetween. In addition,contact portions connected to other transistors, for example, gateelectrodes and source and drain regions in a signal circuit (not shown)are arranged. The gate insulation layer 31 and the gate electrodes 32are overlaid with an insulation layer 81. The above-described contactportions are formed by filling holes arranged in the insulation layer 81with, for example, a conductive material. To form the reflective layer43 in a manner similar to those contact portions, it is difficult tofill a hole 93 because the diameter of the hole 93 is large. Therefore,the reflective layer 43 is arranged so as to cover the inner surface ofthe hole 93.

The reflective layer 43 includes a material that reflects lighttransmitted through each photoelectric conversion section 21 toward thesection 21. For example, the reflective layer 43 includes a materialthat reflects long-wavelength light components, e.g., at leastnear-infrared light and infrared light, toward the photoelectricconversion section 21. The reflective layer 43 may reflectshorter-wavelength light components, such as visible light,near-ultraviolet light, and ultraviolet light, in addition to thelong-wavelength light components. Examples of the materials having theabove-described characteristics include tungsten. It is thereforepreferred that the reflective layer 43 be composed of a single tungstenlayer. Alternatively, it is preferred that the reflective layer 43 becomposed of a laminate containing a tungsten layer. Examples of thelaminates include a laminate including a polysilicon layer and atungsten layer and a laminate including a tungsten layer and a silicidelayer. The reflective layer 43 arranged so as to cover the inner surfaceof the hole 93 has to have a thickness sufficient to preventlong-wavelength light components, such as near-infrared light andinfrared light, from being transmitted through the reflective layer 43.

Since the reflective layer 43 includes the tungsten layer, lighttransmitted through the photoelectric conversion section 21 can bereflected toward the photoelectric conversion section 21. The tungstenlayer is formed without grain growth for an aluminum layer used in therelated art. Accordingly, grain boundaries are hardly generated.Consequently, the reflective layer 43 can reflect long-wavelength lightcomponents, such as near-infrared light and infrared light, which leakfrom grain boundaries in the aluminum layer.

Each hole 93 is filled with a material 44, serving as an insulationlayer or a conductive layer, with the reflective layer 43 therebetween.Since the hole 93 is filled with the material 44 as described above,there is no step in the hole 93.

Further, first interconnection lines 51 to 53 respectively connected tothe contact portions 41 and 42 and the reflective layer 43 are arranged.It is preferred that each first interconnection line 53 connected to thereflective layer 43 have a shape larger than, for example, the shape ofthe reflective layer 43 in plan view. Further, it is preferred that thefirst interconnection lines 51 and 52 be composed of, for example,tungsten. The first interconnection lines 51 and 53 may be composed ofanother metallic material, e.g., copper or aluminum. For example, whenthe first interconnection lines 51 to 53 are formed using tungsten,light which is not completely reflected by the reflective layer 43, forexample, long-wavelength light components leaking from the periphery ofeach area corresponding to the reflective layer 43 can be reflectedtoward the corresponding photoelectric conversion section 21 by thefirst interconnection lines 51 to 53.

Each first interconnection line 51 is connected to a secondinterconnection line 51 through a via hole 54. Each firstinterconnection line 52 is connected to a second interconnection line 62through a via hole 55. Each first interconnection line 53 is connectedto a second interconnection line 63 through a via hole 56. Similarly,each second interconnection line 61 is connected to a thirdinterconnection line 71 through a via hole 64. Each secondinterconnection line 62 is connected to a third interconnection line 72through a via hole 65. Each second interconnection line 63 is connectedto a third interconnection line 73 through a via hole 66. Thesolid-state imaging device 2 of FIG. 2 includes an interconnectionlaminate having three interconnection layers. The present embodiment ofthe invention may be applied to a solid-state imaging device includingan interconnection laminate having four or more interconnection layers.An insulation layer 80, including the insulation layer 81, is arrangedso as to cover the above-described interconnection layers. Theinsulation layer 80 includes a plurality of insulation sublayers inaccordance with the arrangement state of interconnection. The secondsurface of the semiconductor layer 11 is overlaid with the signalcircuit section (not shown) which includes transistors, such as transfertransistors, reset transistors, and amplifier transistors, and theinterconnection laminate including the first interconnection lines 51 to53, the via holes 54 to 56, the second interconnection lines 61 to 63,the via holes 64 to 66, and the third interconnection lines 71 to 73.

In the solid-state imaging device 2 according to the second embodiment,the reflective layer 43 for reflecting light transmitted through eachphotoelectric conversion section 21 toward the section 21 is arrangedadjacent to the second surface of the photoelectric conversion section21 opposite to the first surface thereof, i.e., the second surface ofthe semiconductor layer 11 opposite to the first surface thereof. Iflight entering the photoelectric conversion section 21 is not completelyabsorbed by the photoelectric conversion section 21, particularly,long-wavelength light components that are easily transmitted througheach photoelectric conversion section 21, e.g., near-infrared light andinfrared light can be reflected back to the photoelectric conversionsection 21 by the reflective layer 43. In other words, light transmittedonce through the photoelectric conversion section 21 can be receivedagain by the photoelectric conversion section 21. Consequently, theamount of, particularly, long-wavelength light components received bythe photoelectric conversion section 21 is substantially increased.Thus, the sensitivity of the photoelectric conversion section 21 tolong-wavelength light components can be improved. Since the reflectivelayer 43 is composed of the single tungsten layer or the laminatecontaining the tungsten layer, the density of the reflective layer 43 ishigher than that of an aluminum layer formed by grain growth.Accordingly, the reflective layer 43 can reflect, in particular,long-wavelength light components, such as near-infrared light andinfrared light. Furthermore, among light incident on the first surfaceof the semiconductor layer 11 (i.e., the first surface of thephotoelectric conversion section 21), light components which are notabsorbed by each photoelectric conversion section 21 are reflected backto the photoelectric conversion section 21 by the reflective layer 43included in the signal circuit section in the second surface of thesemiconductor layer 11, thus preventing crosstalk caused by the leakageof light into surrounding pixels.

To make the solid-state imaging device 2 according to the secondembodiment, the contact portion 41 is formed on each gate electrode 32and the contact portion 42 is formed on each pixel isolation region 12.Simultaneously, the reflective layer 43, serving as a contact portionsimilar to those contact portions 41 and 42, may be formed over eachphotoelectric conversion section 21, with the gate insulation layer 31therebetween. Since it is difficult to completely fill the hole 93 witha material for the reflective layer 43, a space on the reflective layer43 in the hole 93 is filled with the material 44, serving as aninsulation layer or a conductive layer. For example, holes 91 and 92 inthe insulation layer 81 are filled with tungsten to form the contactportions 41 and 42. Simultaneously, a tungsten layer is disposed in thehole 93 in the insulation layer 81 over each photoelectric conversionsection 21, thus forming the reflective layer 43. Subsequently, a spaceon the reflective layer 43 in the hole 93 is filled with the material44, serving as an insulation layer or a conductive layer, and thesurplus material 44 is removed.

A solid-state imaging device 3 according to an embodiment (thirdembodiment) of the present invention will now be described withreference to FIGS. 3, 4A, and 4B. FIG. 3 is a schematic cross-sectionalview of the solid-state imaging device 3. FIGS. 4A and 4B are layoutplan views thereof.

Referring to FIGS. 3 to 4B, pixel isolation regions 12 for isolating apixel are arranged in a semiconductor layer 11. The semiconductor layer11 includes, for example, a silicon layer. Each pixel isolation region12 includes, for example, a p-type well region. In each area partitionedby the pixel isolation regions 12, a photoelectric conversion section 21is arranged. On a first surface, through which light enters, of eachphotoelectric conversion section 21 (the lower surface of thephotoelectric conversion section 21 in FIG. 3), i.e., in a first surfaceof the semiconductor layer 11 through which light enters thephotoelectric conversion section 21, a hole storage layer 22 isarranged. The hole storage layer 22 includes, for example, a p+ region.A second surface of the photoelectric conversion section 21 (the uppersurface of the photoelectric conversion section 21 in FIG. 3) oppositeto the first surface thereof, i.e., a second surface of thesemiconductor layer 11 opposite to the first surface thereof includes ahole storage layer 23. Under the hole storage layer 23, an n-type wellregion 24 is arranged. The hole storage layer 23 includes, for example,a p+ region. In addition, a gate electrode (for example, a transfergate) 32 is arranged over the second surface of the photoelectricconversion section 21, with a gate insulation layer 31 therebetween. Inthe semiconductor layer 11, an n+ region 25 is arranged adjacent to oneend of the gate electrode 32, with the gate insulation layer 31therebetween.

A contact portion 41 is arranged on each gate electrode 32. Anothercontact portion 42 is arranged on each pixel isolation region 12. Areflective layer 43 formed simultaneously with the formation of thecontact portions 41 and 42 is arranged over the periphery of eachphotoelectric conversion section 21, with the gate insulation layer 31therebetween. In addition, contact portions connected to othertransistors, for example, gate electrodes and source and drain regionsin a signal circuit section (not shown) are arranged. The gateinsulation layer 31 and the gate electrodes 32 are overlaid with aninsulation layer 81. The above-described contact portions are formed byfilling holes arranged in the insulation layer 81 with, for example, aconductive material. Referring to FIGS. 4A and 4B, a groove 94 to befilled with the conductive material to form the reflective layer 43 isarranged over the periphery of each photoelectric conversion section 21so as to have a predetermined width. FIG. 4A illustrates the positionalrelationship between the photoelectric conversion section 21 and thereflective layer 43 formed in the groove 94. FIG. 4B illustrates thepositional relationship among the photoelectric conversion section 21,the reflective layer 43 in the groove 94, and a first interconnectionline 53.

The reflective layer 43 is composed of a material that reflects lighttransmitted through each photoelectric conversion section 21 toward thesection 21. For example, the reflective layer 43 includes a materialthat reflects long-wavelength light components, e.g., at leastnear-infrared light and infrared light, toward the photoelectricconversion section 21. The reflective layer 43 may reflectshorter-wavelength light components, such as visible light,near-ultraviolet light, and ultraviolet light, in addition to thelong-wavelength light components. Examples of the materials having theabove-described characteristics include tungsten. It is thereforepreferred that the reflective layer 43 be composed of a single tungstenlayer. Alternatively, it is preferred that the reflective layer 43 becomposed of a laminate containing a tungsten layer. Examples of thelaminates include a laminate containing a polysilicon layer and atungsten layer and a laminate containing a tungsten layer and a silicidelayer. The reflective layer 43, which is formed by filling the groove94, has to have a thickness sufficient to prevent long-wavelength lightcomponents, such as near-infrared light and infrared light, from beingtransmitted through the reflective layer 43.

Since the reflective layer 43 includes the tungsten layer, lighttransmitted through the photoelectric conversion section 21 can bereflected toward the photoelectric conversion section 21. The tungstenlayer is formed without grain growth for an aluminum layer used in therelated art. Accordingly, grain boundaries are hardly generated.Consequently, the reflective layer 43 can reflect long-wavelength lightcomponents, such as near-infrared light and infrared light, which leakfrom grain boundaries in the aluminum layer.

Further, first interconnection lines 51 to 53 respectively connected tothe contact portions 41 and 42 and the reflective layer 43 are arranged.It is preferred that each first interconnection line 53 connected to thereflective layer 43 have a shape larger than, for example, the shape ofthe reflective layer 43 in plan view. Further, it is preferred that thefirst interconnection lines 51 and 52 be composed of, for example, asingle tungsten layer or a laminate containing a tungsten layer. Sincethe first interconnection line 53 is composed of the single tungstenlayer or the laminate containing the tungsten layer, long-wavelengthlight components transmitted through an area surrounded by thereflective layer 43 can be reflected toward the correspondingphotoelectric conversion section 21. Furthermore, since the reflectivelayer 43 is arranged over the periphery of each photoelectric conversionsection 21 and is connected to the first interconnection line 53, lightcomponents transmitted through the photoelectric conversion section 21are reflected to the photoelectric conversion section 21 by the firstinterconnection line 53 and the reflective layer 43 without enteringother pixels. Consequently, the light components transmitted through thephotoelectric conversion section 21 can be allowed to again enter thephotoelectric conversion section 21. In other words, since the lightcomponents transmitted through the photoelectric conversion section 21is allowed to again enter the photoelectric conversion section 21 in thethird embodiment, the first interconnection line 53 serves as areflective layer.

The groove 94 in which the reflective layer 43 is formed is arranged soas not to overlap a transfer transistor 101 connected to thephotoelectric conversion section 21. For example, the transfertransistor 101, a reset transistor 102, and an amplifier transistor 103are connected to each photoelectric conversion section 21. In addition,the contact portion 41 connected to a transfer gate 101G of the transfertransistor 101 and contact portions connected to the sources and drainsof the respective transistors are arranged.

Each first interconnection line 51 is connected to a secondinterconnection line 51 through a via hole 54. Each firstinterconnection line 52 is connected to a second interconnection line 62through a via hole 55. Each first interconnection line 53 is connectedto a second interconnection line 63 through a via hole 56. Similarly,each second interconnection line 61 is connected to a thirdinterconnection line 71 through a via hole 64. Each secondinterconnection line 62 is connected to a third interconnection line 72through a via hole 65. Each second interconnection line 63 is connectedto a third interconnection line 73 through a via hole 66. Thesolid-state imaging device 3 of FIG. 3 includes an interconnectionlaminate having three interconnection layers. The present embodiment ofthe invention may be applied to a solid-state imaging device includingan interconnection laminate having four or more interconnection layers.An insulation layer 80, including the insulation layer 81, is arrangedso as to cover the above-described interconnection layers. Theinsulation layer 80 includes a plurality of insulation sublayers inaccordance with the arrangement state of interconnection. The secondsurface of the semiconductor layer 11 is overlaid with the signalcircuit section (not shown) which includes transistors, such as thetransfer transistors 101, the reset transistors 102, and the amplifiertransistors 103, and the interconnection laminate including the firstinterconnection lines 51 to 53, the via holes 54 to 56, the secondinterconnection lines 61 to 63, the via holes 64 to 66, and the thirdinterconnection lines 71 to 73.

In the solid-state imaging device 3 according to the third embodiment,the reflective layer 43 and the first interconnection line 53 forreflecting light components transmitted through each photoelectricconversion section 21 toward the section 21 are arranged adjacent to thesecond surface of the photoelectric conversion section 21 opposite tothe first surface thereof, i.e., the second surface of the semiconductorlayer 11 opposite to the first surface thereof. If light entering thephotoelectric conversion section 21 is not completely absorbed by thephotoelectric conversion section 21, particularly, long-wavelength lightcomponents that are easily transmitted through each photoelectricconversion section 21, e.g., near-infrared light and infrared light canbe reflected back to the photoelectric conversion section 21 by thereflective layer 43 and the first interconnection line 53. In otherwords, light transmitted once through the photoelectric conversionsection 21 can be received again by the photoelectric conversion section21. Consequently, the amount of, particularly, long-wavelength lightcomponents received by the photoelectric conversion section 21 issubstantially increased. Thus, the sensitivity of the photoelectricconversion section 21 to long-wavelength light components can beimproved. Since the reflective layer 43 and the first interconnectionline 53 are each composed of the single tungsten layer or the laminatecontaining the tungsten layer, the density of each of the reflectivelayer 43 and the first interconnection line 53 is higher than that of analuminum layer formed by grain growth. Accordingly, the reflective layer43 and the first interconnection line 53 can reflect, in particular,long-wavelength light components, such as near-infrared light andinfrared light. Furthermore, among light incident on the first surfaceof the semiconductor layer 11 (i.e., the first surface of thephotoelectric conversion section 21), light components which are notabsorbed by each photoelectric conversion section 21 are reflected backto the photoelectric conversion section 21 by the reflective layer 43and the first interconnection line 53 included in the signal circuitsection in the second surface of the semiconductor layer 11, thuspreventing crosstalk caused by the leakage of light into surroundingpixels.

To make the solid-state imaging device 3 according to the thirdembodiment, the contact portion 41 is formed on each gate electrode 32and the contact portion 42 is formed on each pixel isolation region 12.Simultaneously, the reflective layer 43, serving as a contact portionsimilar to those contact portions 41 and 42, may be formed over eachphotoelectric conversion section 21, with the gate insulation layer 31therebetween. For example, holes 91 and 92 arranged in the insulationlayer 81 are filled with tungsten to form the contact portions 41 and42. Simultaneously, the groove 94 in the insulation layer 81 over eachphotoelectric conversion section 21 is filled with tungsten, thusforming the reflective layer 43. After that, the first interconnectionline 53 connected to the reflective layer 43 is formed so as to coverthe photoelectric conversion section 21 simultaneously with theformation of the first interconnection lines 51 and 52 connected to thecontact portions 41 and 42, respectively.

A solid-state imaging device 4 according to an embodiment (fourthembodiment) of the present invention will now be described withreference to FIG. 5, which is a schematic cross-sectional view of thesolid-state imaging device 4.

Referring to FIG. 5, pixel isolation regions 12 for isolating a pixelare arranged in a semiconductor layer 11. The semiconductor layer 11includes, for example, a silicon layer. Each pixel isolation region 12includes, for example, a p-type well region. In each area partitioned bythe pixel isolation regions 12, a photoelectric conversion section 21 isarranged. On a first surface, through which light enters, of eachphotoelectric conversion section 21 (the lower surface of thephotoelectric conversion section 21 in FIG. 5), i.e., in a first surfaceof the semiconductor layer 11 through which light enters thephotoelectric conversion section 21, a hole storage layer 22 isarranged. The hole storage layer 22 includes, for example, a p+ region.A second surface of the photoelectric conversion section 21 (the uppersurface of the photoelectric conversion section 21 in FIG. 5) oppositeto the first surface thereof, i.e., a second surface of thesemiconductor layer 11 opposite to the first surface thereof includes ahole storage layer 23. Under the hole storage layer 23, an n-type wellregion 24 is arranged. The hole storage layer 23 includes, for example,a p+ region. In addition, a gate electrode (for example, a transfergate) 32 is arranged over the second surface of the photoelectricconversion section 21, with a gate insulation layer 31 therebetween. Inthe semiconductor layer 11, an n+ region 25 is arranged adjacent to oneend of the gate electrode 32, with the gate insulation layer 31therebetween.

Further, an electrode layer 34 formed by the same layer as that for thegate electrode 32 is arranged over each photoelectric conversion section21, with the gate insulation layer 31 therebetween. The electrode layer34 is composed of, for example, polysilicon. Alternatively, theelectrode layer 34 may be composed of polycide. A contact portion 41 isconnected to each gate electrode 32, contact portions are connected toother transistors, for example, gate electrodes and source and drainregions in a signal circuit section (not shown), and a contact potion 42is connected to each pixel isolation regions 12. In addition, aplurality of reflective layer segments 43, serving as contact portions,are arranged on the electrode layer 34. The reflective layer segments 43are arranged as many as possible on the electrode layer 34. Thereflective layer segments 43 are each composed of a material thatreflects light transmitted through each photoelectric conversion section21 toward the section 21. For example, the reflective layer segments 43include a material that reflects long-wavelength light components, suchas near-infrared light and infrared light, toward the photoelectricconversion section 21. The reflective layer segments 43 may reflectshorter-wavelength light components, such as visible light,near-ultraviolet light, and ultraviolet light, in addition to thelong-wavelength light components. Examples of the materials having theabove-described characteristics include tungsten. It is thereforepreferred that the reflective layer segments 43 be composed of a singletungsten layer. Alternatively, it is preferred that the reflective layersegments 43 be composed of a laminate containing a tungsten layer. Thereflective layer segments 43 on the electrode layer 34 are arranged sothat the distance between the neighboring segments is minimized inaccordance with the design rule and the diameter of each reflectivelayer segment 43 is maximized in accordance with the design rule. Inother words, the reflective layer segments 43 are arranged so that thetotal area occupied by the reflective layer segments 43 on the electrodelayer 34 is maximized.

Further, first interconnection lines 51 to 53 respectively connected tothe contact portions 41 and 42 and the reflective layer segments 43 arearranged. It is preferred that each first interconnection line 53connected to the reflective layer segments 43 have a shape similar to orlarger than that of the electrode layer 34. Further, the firstinterconnection lines 51 and 52 are composed of, for example, a singletungsten layer or a laminate containing a tungsten layer. Since thefirst interconnection line 53 is formed by the single tungsten layer orthe laminate containing the tungsten layer, long-wavelength lightcomponents transmitted through each portion between the reflective layersegments 43 can be reflected toward the corresponding photoelectricconversion section 21. Furthermore, since light transmitted through eachphotoelectric conversion section 21 is reflected toward the section 21by the first interconnection line 53 and the reflective layer segments43, the amount of light entering other pixels can be reduced and thereflected light can be allowed to again enter the photoelectricconversion section 21. In other words, since light transmitted throughthe photoelectric conversion section 21 is allowed to again enter thephotoelectric conversion section 21 in accordance with the fourthembodiment, the first interconnection line 53 also serves as areflective layer.

Each first interconnection line 51 is connected to a secondinterconnection line 51 through a via hole 54. Each firstinterconnection line 52 is connected to a second interconnection line 62through a via hole 55. Each first interconnection line 53 is connectedto a second interconnection line 63 through a via hole 56. Similarly,each second interconnection line 61 is connected to a thirdinterconnection line 71 through a via hole 64. Each secondinterconnection line 62 is connected to a third interconnection line 72through a via hole 65. Each second interconnection line 63 is connectedto a third interconnection line 73 through a via hole 66. Thesolid-state imaging device 4 of FIG. 5 includes an interconnectionlaminate having three interconnection layers. The present embodiment ofthe invention may be applied to a solid-state imaging device includingan interconnection laminate having four or more interconnection layers.An insulation layer 81 is arranged so as to cover the above-describedinterconnection layers. The insulation layer 81 includes a plurality ofinsulation sublayers in accordance with the arrangement state ofinterconnection. The second surface of the semiconductor layer 11 isoverlaid with the signal circuit section (not shown) which includestransistors, such as transfer transistors, reset transistors, andamplifier transistors, and the interconnection laminate including thefirst interconnection lines 51 to 53, the via holes 54 to 56, the secondinterconnection lines 61 to 63, the via holes 64 to 66, and the thirdinterconnection lines 71 to 73.

In the solid-state imaging device 4 according to the fourth embodiment,the reflective layer segments 43 for reflecting light transmittedthrough each photoelectric conversion section 21 toward the section 21are arranged adjacent to the second surface of the photoelectricconversion section 21 opposite to the first surface thereof, i.e., thesecond surface of the semiconductor layer 11 opposite to the firstsurface thereof. If light entering the photoelectric conversion section21 is not completely absorbed by the photoelectric conversion section21, particularly, long-wavelength light components that are easilytransmitted through each photoelectric conversion section 21, e.g.,near-infrared light and infrared light can be reflected back to thephotoelectric conversion section 21 by the reflective layer segments 43.In other words, light transmitted once through the photoelectricconversion section 21 can be received again by the photoelectricconversion section 21. Consequently, the amount of, particularly,long-wavelength light components received by the photoelectricconversion section 21 is substantially increased. Thus, the sensitivityof the photoelectric conversion section 21 to long-wavelength lightcomponents can be improved. Since the reflective layer segments 4 arecomposed of the single tungsten layer or the laminate containing thetungsten layer, the density of each reflective layer segment 43 ishigher than that of an aluminum layer formed by grain growth.Accordingly, the reflective layer segments 43 can reflect, inparticular, long-wavelength light components, such as near-infraredlight and infrared light. Furthermore, among light incident on the firstsurface of the semiconductor layer 11 (i.e., the first surface of thephotoelectric conversion section 21), light components which are notabsorbed by each photoelectric conversion section 21 are reflected backto the photoelectric conversion section 21 by the reflective layersegments 43 adjacent included in the signal circuit section in thesecond surface of the semiconductor layer 11, thus preventing crosstalkcaused by the leakage of light into surrounding pixels.

In addition, applying a bias voltage to the electrode layer 34 enablesthe potential of a charge storage portion in the photoelectricconversion section 21 to vary. In current CMOS image sensors, thepotential depth of the charge storage portion has to be designed so thatsignal charge is completely transferred upon reading the signal chargewithout leaving the signal charge to be read, that is, without any imagelag. According to the present embodiment of the invention, when signalcharge is read out, a bias voltage is applied to make the potentialdepth of the charge storage portion shallower, thus maintaining theenough potential depth of the charge storage portion while keeping thereadout efficiency constant. Consequently, the amount of saturationcharge can be increased.

Since the electrode layer 34, to which a bias voltage can be applied, isarranged over each photoelectric conversion section 21, this arrangementserves as a countermeasure against pinning. If the electrode layer 34 ismade of polysilicon, the electrode layer 34 has an insufficient functionas a reflective layer. According to the present embodiment, however, thereflective layer segments 43, each of which has a structure similar to acontact portion and is made of tungsten, are arranged on the electrodelayer 34. Therefore, the reflecting efficiency can be ensured.

To make the solid-state imaging device 4 according to the fourthembodiment, in the step of forming the gate electrode 32 over eachphotoelectric conversion section 21, the electrode layer 34 is formed onthe gate insulation layer 31 over the photoelectric conversion section21. In other words, when the gate electrodes of transistors, such as thetransfer transistor, the reset transistor, and the amplifier transistor,are formed, the electrode layer 34 is also formed. Further, when thecontact portion 41 is formed on the gate electrode 32 and the contactportion 42 is formed on the pixel isolation regions 12, the reflectivelayer segments 43 including the contact portions similar to the contactportions 41 and 42 may be formed on the electrode layer 34. For example,holes 91 and 92 arranged in the insulation layer 81 are filled withtungsten to form the contact portions 41 and 42. Simultaneously, aplurality of holes 93 in the insulation layer 81 over each photoelectricconversion section 21 are filled with tungsten, thus forming thereflective layer segments 43. At that time, the reflective layersegments 43 are formed on the electrode layer 34 so that the distancebetween neighboring segments is minimized in accordance with the designrule and the diameter of each segment is maximized. In other words, thereflective layer segments 43 are formed so that the total area occupiedby the reflective layer segments 43 on the electrode layer 34 ismaximized.

A solid-state imaging device 5 according to an embodiment (fifthembodiment) of the present invention will now be described withreference to FIG. 6, which is a schematic cross-sectional view of thesolid-state imaging device 5.

Referring to FIG. 6, pixel isolation regions 12 for isolating a pixelare arranged in a semiconductor layer 11. The semiconductor layer 11includes, for example, a silicon layer. Each pixel isolation region 12includes, for example, a p-type well region. In each area partitioned bythe pixel isolation regions 12, a photoelectric conversion section 21 isarranged. On a first surface, through which light enters, of eachphotoelectric conversion section 21 (the lower surface of thephotoelectric conversion section 21 in FIG. 6), i.e., in a first surfaceof the semiconductor layer 11 through which light enters thephotoelectric conversion section 21, a hole storage layer 22 isarranged. The hole storage layer 22 includes, for example, a p+ region.A second surface of the photoelectric conversion section 21 (the uppersurface of the photoelectric conversion section 21 in FIG. 6) oppositeto the first surface thereof, i.e., a second surface of thesemiconductor layer 11 opposite to the first surface thereof includes ahole storage layer 23. Under the hole storage layer 23, an n-type wellregion 24 is arranged. The hole storage layer 23 includes, for example,a p+ region. Further, a gate electrode (for example, a transfer gate) 32is arranged over the second surface of the photoelectric conversionsection 21, with a gate insulation layer 31 therebetween. In thesemiconductor layer 11, an n+ region 25 is arranged adjacent to one endof each gate electrode 32, with the gate insulation layer 31therebetween.

A contact portion 41 is arranged on each gate electrode 32. A reflectivelayer 43, formed by filling a groove 95 arranged so as to surround theperiphery of each photoelectric conversion section 21, is arranged oneach pixel isolation regions 12. In addition, contact portions connectedto other transistors, e.g., gate electrodes and source and drain regionsin a signal circuit section (not shown) are arranged. The gateinsulation layer 31 and the gate electrodes 32 are overlaid with aninsulation layer 81. The respective contact portions and the reflectivelayer 43 are formed by filling holes and the groove 95 arranged in theinsulation layer 81 with, for example, a conductive material.

The reflective layer 43 is made of a material that reflects lighttransmitted through each photoelectric conversion sections 21 toward thesection 21. For example, the reflective layer 43 includes a materialthat reflects long-wavelength light components, e.g., at leastnear-infrared light and infrared light components toward thephotoelectric conversion section 21. The reflective layer 43 may reflectshorter-wavelength light components, such as visible light,near-ultraviolet light, and ultraviolet light, in addition to thelong-wavelength light components. Examples of the materials having theabove-described characteristics include tungsten. It is thereforepreferred that the reflective layer 43 be composed of a single tungstenlayer. Alternatively, it is preferred that the reflective layer 43 becomposed of a laminate containing a tungsten layer. Examples of thelaminates include a laminate containing a polysilicon layer and atungsten layer and a laminate containing a tungsten layer and a silicidelayer. The reflective layer 43 obtained by filling the groove 95 has tohave a thickness sufficient to prevent long-wavelength light components,such as near-infrared light and infrared light, from being transmittedthrough the reflective layer 43.

Since the reflective layer 43 includes the tungsten layer, lighttransmitted through the photoelectric conversion section 21 can bereflected toward the photoelectric conversion section 21. The tungstenlayer is formed without grain growth for an aluminum layer used in therelated art. Accordingly, grain boundaries are hardly generated.Consequently, the reflective layer 43 can reflect long-wavelength lightcomponents, such as near-infrared light and infrared light, which leakfrom grain boundaries in the aluminum layer.

Further, first interconnection lines 51 are connected to the contactportions 41 and first interconnection lines 53 are connected to thereflective layer 43. It is preferred that each first interconnectionline 53 connected to the reflective layer 43 have a shape similar to orlarger than that of the reflective layer 43 surrounding thephotoelectric conversion section 21. Further, the first interconnectionlines 51 and 53 are composed of a single tungsten layer or a laminatecontaining a tungsten layer. Since each first interconnection line 53 isformed using the single tungsten layer or the laminate containing thetungsten layer, long-wavelength light components transmitted through anarea surrounding the reflective layer 43 can be reflected toward thephotoelectric conversion section 21. Since the reflective layer 43 isarranged so as to surround the periphery of each photoelectricconversion section 21 and is connected to the first interconnectionlines 53, light transmitted through the photoelectric conversion section21 are reflected toward the photoelectric conversion section 21 by thefirst interconnection lines 53 and the reflective layer 43. Thereflected light components can be allowed to again enter thephotoelectric conversion section 21 without entering other pixels. Inother words, since the first interconnection lines 53 each have afunction of allowing light transmitted through the photoelectricconversion sections 21 to again enter the photoelectric conversionsections 21, each first interconnection line 53 also serves as areflective layer.

The first interconnection lines 51 and 53 are connected to secondinterconnection lines 61 and 62 through via holes 54 and 55,respectively. Similarly, the second interconnection lines 61 and 62 areconnected to third interconnection lines 71 and 72 through via holes 64and 65, respectively. The solid-state imaging device 5 of FIG. 6includes an interconnection laminate having three interconnectionlayers. The present embodiment of the invention may be applied to asolid-state imaging device including an interconnection laminate havingfour or more interconnection layers. An insulation layer 80, includingthe insulation layer 81, is arranged so as to cover the above-describedinterconnection layers. The insulation layer 80 includes a plurality ofinsulation sublayers in accordance with the arrangement state ofinterconnection. The second surface of the semiconductor layer 11 isoverlaid with the signal circuit section (not shown) which includestransistors, such as transfer transistors, reset transistors, andamplifier transistors, and the interconnection laminate including thefirst interconnection lines 51 and 53, the via holes 54 and 55, thesecond interconnection lines 61 and 62, the via holes 64 and 65, and thethird interconnection lines 71 and 72.

In the solid-state imaging device 5 according to the fifth embodiment,the reflective layer 43 and the first interconnection lines 53 forreflecting light transmitted through each photoelectric conversionsection 21 toward the section 21 are arranged adjacent to the secondsurface of the photoelectric conversion section 21 opposite to the firstsurface thereof, i.e., the second surface of the semiconductor layer 11opposite to the first surface thereof. If light entering thephotoelectric conversion section 21 is not completely absorbed by thephotoelectric conversion section 21, particularly, long-wavelength lightcomponents that are easily transmitted through each photoelectricconversion section 21, e.g., near-infrared light and infrared light canbe reflected back to the photoelectric conversion section 21 by thereflective layer 43 and the first interconnection lines 53. In otherwords, light transmitted once through the photoelectric conversionsection 21 can be received again by the photoelectric conversion section21. Consequently, the amount of, particularly, long-wavelength lightcomponents received by the photoelectric conversion section 21 issubstantially increased. Thus, the sensitivity of the photoelectricconversion section 21 to long-wavelength light components can beimproved. Since the reflective layer 43 and the first interconnectionline 53 are each composed of the single tungsten layer or the laminatecontaining the tungsten layer, the density of each of the reflectivelayer 43 and the first interconnection lines 53 is higher than that ofan aluminum layer obtained by grain growth. Accordingly, the reflectivelayer 43 and the first interconnection lines 53 can reflect, inparticular, long-wavelength light components, such as near-infraredlight and infrared light. Furthermore, among light incident on the firstsurface of the semiconductor layer 11 (i.e., the first surface of thephotoelectric conversion section 21), light components which are notabsorbed by each photoelectric conversion section 21 are reflected backto the photoelectric conversion section 21 by the reflective layer 43and the first interconnection lines 53 included in the signal circuitsection in the second surface of the semiconductor layer 11, thuspreventing crosstalk caused by the leakage of light into surroundingpixels.

To make the solid-state imaging device 5 according to the fifthembodiment, when the contact portion 41 is formed on each gate electrode32, the reflective layer 43, serving as a contact portion, may be formedon each pixel isolation region 12 in a manner similar to the contactportion 41 on the gate electrode 32. For example, a hole 91 in theinsulation layer 81 is filled with tungsten to form the contact portion41. Simultaneously, the groove 95 in the insulation layer 81 on eachpixel isolation region 12 is filled with tungsten, thus forming thereflective layer 43. Subsequently, the first interconnection lines 53are arranged so as to be connected to the reflective layer 43 over thephotoelectric conversion section 21 simultaneously with forming thefirst interconnection lines 51 so as to be connected to the contactportions 41.

In each of the above-described solid-state imaging devices 1 to 5, thereflective layer (or reflective layer segment) 43 is made of tungsten.The reflective layer 43 may be composed of a laminate containing atungsten layer underlaid with a silicide layer or a laminate containinga tungsten layer underlaid with a polysilicon layer. In the use of thislaminate structure, the silicide or polysilicon layer can preventprocessing damage on an underlying layer, the damage being caused byprocessing using tungsten.

An imaging apparatus 200 according to an embodiment (application) of thepresent invention will now be described with reference to FIG. 7, whichis a block diagram of the imaging apparatus 200.

Referring to FIG. 7, the imaging apparatus 200 includes an imaging unit201 that includes a solid-state imaging device (not shown). The imagingapparatus 200 further includes an imaging optical system 202 for imageformation. The imaging optical system 202 is arranged on the lightcollection side upstream of the imaging unit 201. The imaging unit 201is connected to a signal processing unit 203, which includes a drivingcircuit for driving the imaging unit 201 and a signal processing circuitfor processing signals, obtained by photoelectric conversion by thesolid-state imaging device, to generate image signals. The image signalsobtained by the signal processing unit 203 can be stored in an imagestorage unit (not shown). The imaging apparatus 200 may include any ofthe solid-state imaging devices 1 to 5 described in the foregoingembodiments.

Since the imaging apparatus 200 according to the present embodimentincludes any of the solid-state imaging devices 1 to 5 according to theforegoing embodiments, the photoelectric conversion section in eachpixel can have an enough area as described above. Advantageously, thecharacteristics of each pixel, e.g., the sensitivity can be improved.

The structure of the imaging apparatus 200 according to the presentembodiment is not limited to the above-described structure. The presentembodiment of the invention may be applied to any imaging apparatusincluding a solid-state imaging device.

Each of the above-described solid-state imaging devices 1 to 5 may beimplemented as a single chip or a module having an imaging functionachieved by the imaging unit, the signal processing unit, and theoptical system which are integrated into a single package. The presentinvention can be applied not only to a solid-state imaging device, butalso to an imaging apparatus. In this case, the imaging apparatus havinghigh image quality can be provided. In this instance, the “imagingapparatus” means a portable device having, for example, a camera or animaging function. The term “imaging” includes not only image capture ina typical camera shooting mode but also fingerprint detection in a broadsense.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A solid-state imaging device comprising: a photoelectric conversionsection arranged in a semiconductor layer having a first surface throughwhich light enters the photoelectric conversion section; a signalcircuit section arranged in a second surface of the semiconductor layeropposite to the first surface, the signal circuit section processingsignal charge obtained by photoelectric conversion by the photoelectricconversion section; and a reflective layer arranged on the secondsurface of the semiconductor layer opposite to the first surface, thereflective layer reflecting light transmitted through the photoelectricconversion section back thereto, wherein the reflective layer iscomposed of a single tungsten layer or a laminate containing a tungstenlayer.
 2. The device according to claim 1, wherein the reflective layeris formed by filling a hole arranged in an insulation layer over thephotoelectric conversion section.
 3. The device according to claim 1,wherein the reflective layer is arranged on at least the inner surfaceof a hole arranged in an insulation layer over the photoelectricconversion section.
 4. The device according to claim 1, furthercomprising: a polysilicon electrode layer over the photoelectricconversion section, with an insulation layer therebetween, wherein thereflective layer is arranged on the polysilicon electrode layer.
 5. Thedevice according to claim 4, wherein the polysilicon electrode layer isapplied with a bias voltage through the reflective layer.
 6. The deviceaccording to claim 1, wherein the reflective layer is arranged over theperiphery of the photoelectric conversion section, and aninterconnection layer connected to the reflective layer extends over thephotoelectric conversion section.
 7. The device according to claim 6,wherein the interconnection layer extending over the photoelectricconversion section has a function of reflecting light transmittedthrough the photoelectric conversion section back thereto, and theinterconnection layer is composed of a single tungsten layer or alaminate containing a tungsten layer.
 8. A method of making asolid-state imaging device, comprising the steps of: (a) forming aphotoelectric conversion section in a semiconductor layer having a firstsurface through which light enters the photoelectric conversion section;and (b) forming a signal circuit section in a second surface of thesemiconductor layer opposite to the first surface, the signal circuitsection including transistors for extracting an electrical signalobtained by photoelectric conversion by the photoelectric conversionsection, wherein the step (b) includes the substep of forming a contactportion connected to each transistor in the signal circuit section, andin the substep, a reflective layer is formed on the second surface ofthe semiconductor layer opposite to the first surface, the reflectivelayer reflecting light transmitted through the photoelectric conversionsection back thereto and being composed of a single tungsten layer or alaminate containing a tungsten layer.
 9. The method according to claim8, wherein the reflective layer is formed in the substep of forming acontact portion connected to each transistor in the signal circuitsection, and the step (b) further includes the substep of forming aninterconnection layer connected to each contact portion such that theinterconnection layer extends over the photoelectric conversion section.10. An imaging apparatus comprising: a collection optical unit thatcollects incident light; a solid-state imaging device that receives thelight collected by the collection optical unit and converts the lightinto an electrical signal; and a signal processing unit that processesthe electrical signal, wherein the solid-state imaging device includes aphotoelectric conversion section arranged in a semiconductor layerhaving a first surface through which light enters the photoelectricconversion section, a signal circuit section arranged in a secondsurface of the semiconductor layer opposite to the first surface, thesignal circuit section extracting the electrical signal obtained by thephotoelectric conversion section, and a reflective layer arranged on thesecond surface of the semiconductor layer opposite to the first surface,the reflective layer reflecting light transmitted through thephotoelectric conversion section back thereto, and the reflective layeris composed of a single tungsten layer or a laminate containing atungsten layer.